> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mellea.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# mellea.stdlib.requirements.tool_reqs

> [`Requirement`](../../core/requirement#class-requirement) factories for tool-use validation.

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[`Requirement`](../../core/requirement#class-requirement) factories for tool-use validation.

Provides `uses_tool`, a [`Requirement`](../../core/requirement#class-requirement) factory that validates whether a model
response includes a call to a specified tool — useful when you need to enforce tool
invocation via rejection sampling rather than relying solely on the model's
`tool_choice` setting. Also provides `tool_arg_validator`, which validates the
value of a specific argument to a named tool. Both accept either the tool's string
name or its callable.

## Functions

<div className="w-full h-px bg-gray-200 dark:bg-gray-700 my-4" />

### <span className="ml-2 inline-flex items-center rounded-full px-2 py-1 text-[0.7rem] font-bold tracking-wide bg-[#3064E3]/20 text-[#1D4ED8]">FUNC</span> `uses_tool` <sup><a href="https://github.com/generative-computing/mellea/blob/v0.6.0/mellea/stdlib/requirements/tool_reqs.py#L26" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python theme={null}
uses_tool(tool_name: str | Callable, check_only: bool = False) -> Requirement
```

Forces the model to call a given tool.

**Args:**

* `tool_name`: The tool that must be called; this can be either the name of the tool or the Callable for the tool.
* `check_only`: Propagates to the Requirement.

Use `tool_choice` if the OpenAI `tool_choice` model option is supported by your model and inference engine.

**Returns:**

* A [`Requirement`](../../core/requirement#class-requirement) that validates whether the specified tool was called.

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### <span className="ml-2 inline-flex items-center rounded-full px-2 py-1 text-[0.7rem] font-bold tracking-wide bg-[#3064E3]/20 text-[#1D4ED8]">FUNC</span> `tool_arg_validator` <sup><a href="https://github.com/generative-computing/mellea/blob/v0.6.0/mellea/stdlib/requirements/tool_reqs.py#L54" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python theme={null}
tool_arg_validator(description: str, tool_name: str | Callable | None, arg_name: str, validation_fn: Callable, check_only: bool = False) -> Requirement
```

A requirement that passes only if `validation_fn` returns a True value for the *value* of the `arg_name` argument to `tool_name`.

If `tool_name` is not specified, then this requirement is enforced for *every* tool that was called.

**Args:**

* `description`: The Requirement description.
* `tool_name`: The (optional) tool name to validate. When None, all tools are checked.
* `arg_name`: The argument to check.
* `validation_fn`: A validation function for validating the value of the `arg_name` argument.
* `check_only`: propagates the `check_only` flag to the requirement.

**Returns:**

* A [`Requirement`](../../core/requirement#class-requirement) that validates the specified tool argument.

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